The invention relates to a non-return valve for an oil return in the crankcase ventilation system of a combustion engine, including a valve housing and a valve body which is mounted in the valve housing so as to be displaceable between an open position and a closed position, the valve body in the non-operating state of the combustion engine being maintained in the open position without preload and being configured to automatically move to the closed position in case of an overpressure at the crankcase side with respect to the oil separator chamber.
To reliably prevent the ingress of oil from the crankcase through the oil return into the cleanroom of the oil separator, and thus into the intake section, conventionally for example a siphon is arranged in the oil return, see DE 198 13 702 C1; DE 20 2004 004 803 U1, FIG. 7; DE 10 2004 006 082 A1. As at any time there is some oil in the siphon, the oil return runs the risk to freeze and consequently to become inoperative. The same applies to the embodiment according to FIG. 13 of DE 20 2004 004 803 U1, in which a sintered body is arranged in the oil return.
In addition, non-return valves are commonly known for the oil return of an oil separator in the crankcase ventilation system of a combustion engine.
Common types of non-return valves for example comprise an umbrella-shaped or plate-shaped elastomer body which in the neutral position of the engine is in the closed position, and which in case of a low pressure in the crankcase and/or at a predetermined level in an oil reservoir opens automatically, see U.S. Pat. No. 4,602,595; WO 98 32955 A1; DE 10 2004 002 310 A1; DE 20 2004 004 803 U1, FIG. 14; WO 2004 090292 A2. This non-generic design runs the risk to freeze in the non-operating state of the engine, as the oil cannot discharge.
The like applies to conventional flexible-tongue valves which in the neutral position of the engine are in the closed position, and which in case of a low pressure in the crankcase and/or at a predetermined level in an oil reservoir open automatically, see DE 10 2004 061 938 B3; EP 1 614 871 A2; DE 10 2006 038 700 A1, FIG. 4; DE 10 2008 030 134 A1; DE 10 2007 058 059 A1; DE 10 2007 008 672 A1; DE 10 2008 019 293 A1.
The spring diaphragm according to DE 296 05 425 U1 in the unloaded state owing to its own weight in fact is in an open position. However, the spring diaphragm in the open position hangs down loose so that the open position is not well-defined. For example, the flexible tongue cannot be prevented from sagging due to aging or high stress, being a potential risk to the operational capability of the non-return valve.
DE 20 2007 011 585 U1 discloses an oil return valve comprising a floating body located in a housing, which being subject to buoyant lift uncovers a discharge opening in the housing when a defined oil level is exceeded, and which being subject to gravity covers said opening when the oil level falls below a defined oil level.
EP 1 090 210 B1 discloses a cyclone separator comprising a valve ball arranged in the oil return, which being subject to gravity in the non-operating state of the engine closes the oil return.
All of the above-mentioned non-return valves have in common that in the non-operating state of the engine they do not provide the maximum opening diameter, being detrimental to the freezing behavior.
Another likewise non-generic design provides a controlled non-return valve which is opened in a pilot-operated manner by use of external power, for example compressed air or magnetic force, see DE 195 15 482 A1; DE 202 17 601 U1; DE 203 02 911 U1; DE 10 2004 018 567 B3. However, the realization of such pilot-operated valves is very complex. The same applies to flexible-tongue valves controlled by a pump according to DE 20 2004 004 802 U1 and DE 10 2008 019 293 A1.
A generic oil return non-return valve is known from DE 196 28 812 B4. The non-return valve includes a housing and a valve body which is mounted within the housing so as to be movable as a whole, the valve body in the non-operating state of the engine uncovering a maximum opening diameter, and during operation in case of an overpressure in the crankcase being lifted relative to the oil separator covering a through opening. This valve is inserted into a mounting of the crankcase, and there are provided circumferential sealing lips around the outer circumference of the valve housing having an outer diameter that is slightly larger than the diameter of the mounting so that the housing can be fittingly inserted into the mounting with frictional contact performing a sealing function and being adjustable. However, depending on the mounting position it is difficult to find a place for the non-return valve in the crankcase. Furthermore, the non-return valve for the engine manufacturer is an additional component to be mounted. Removing the non-return valve from the crankcase in the event of malfunction or failure, after all, involves great effort.